Multicast frustration.

21012009

Ugh! Just been doing some testing with PIM sparse mode and run up against what is probably a code issue.

The situation – two routers connected together over ethernet. R1 has ‘ip igmp join-group 230.0.0.1’ on its ethernet interface – this makes it a listener for that group. R2 is a PIM bootstrap router (BSR) and rendezvous point (RP). Now, I should be able to ping 230.0.0.1 from R2 and receive a response, but I wasn’t getting anything.

I knew that R1 had joined the group because if I type ‘show ip igmp group’ I can see that R1 has registered:

So – the listening router is a 7206VXR, running 12.2(25)S9. I decided to take the config off, and replace it with a 3725 on 12.4(5c) – the only difference being the IP address ends in .8 instead of .6. For some reason, I started getting ping responses, but the output interface is still null:

Hmm – after writing this up, I am thinking that the olist being ‘null’ for fa1/0 is probably OK. Since this is the ethernet connection going to the other router, there’s no need to have an olist – the standard routing table takes care of which interface to send the packet out of. For the second ping that was sourced from 1.1.1.1 (lo0), there *is* a need to have an entry on the outgoing interface list – presumably this tells the router which interface it has received a ‘join’ message on, and therefore needs to have the multicast stream sent out of.

Oddly, I can’t get any output from ‘debug ip mpacket’ on the listening router – either the 7206 or the 3725. I’ve looked at this for so long (and boiled it down to basics from something more complex) that I think I’ll go to bed with a headache now! Another day, maybe I’ll understand what the hell is going on…